#include <iostream>
using namespace std;
 
// 变量声明
 extern int a, b;
 extern int c;
 extern float f;
   
int main ()
{
  // 变量定义
  int a, b;
  int c;
  float f;

  // 实际初始化
  a = 10;
  b = 20;
  c = a + b;

  cout << c << endl ;

  f = 70.0/3.0;
  cout << f << endl ;

  return 0;
}

